The investigation of cell lines derived from human teratocarcinomas can provide information pertinent to the characteristics of human embryonic cells, as well as knowledge essential for improving methods for clinically managing these tumors. Of crucial importance is the definition of the embryonal carcinoma (EC) stem cells and analysis of their properties. Previously, we cloned a line of human EC cells, 2102Ep, which undergoes limited differentiation along a trophoblastic lineage in culture. These studies have shown that human EC cells, in contrast with their murine counterparts, express the cell surface antigen SSEA-3, but not SSEA-1, low levels of HLA-A,B,C and beta-2-microglobulin, and also EGF receptor. Spontaneous differentiation under some culture conditions leads to the appearance of SSEA-1-positive cells, which synthesize fibronectin, and also a small number of cells with the ultrastructural features of trophoblastic giant cells and cytoplasmic HCG. Further work has now led to the identification of a new monoclonal antibody-defined antigenic determinant, SSEA-4, also characteristically expressed by human EC cells. Both SSEA-3 and SSEA-4 epitopes are contained within a group of globoseries oligosaccharides occurring as glycosphingolipids in the plasma membrane of these cells. They are thus related to the P-blood group system and are also found on red blood cells but few other cell types. Other monoclonal antibodies raised to human EC cells include two defining epitopes associated with the liver isozyme of alkaline phosphatase, an enzyme strongly expressed on the surface of human EC cells; two antibodies, TRA-1-60 and TRA-1-81, defining two new epitopes characteristic of human EC cells; and also two defining widely distributed antigens encoded by genes on human chromosomes 1 and 11. A second series of cloned human EC cells derived from the teratocarcinoma line TERA-2 have been characterized. Most of these cells express the characteristic properties of human EC cells, but, unlike the other available lines, they are able to differentiate into a variety of somatic cell types: injected into nude mice they form tumors containing glandular structures and neural elements as well as nests of EC cells; in culture, they can be induced to differentiate into various cells, including neurons, by exposure to retinoic acid. This differentiation is irreversible and accompanied by the loss of the human EC cell characteristics. Among the differentiated cells are those permissive for HCMV replication; a virus responsible for a variety of birth defects associated with the nervous system; the EC cells are not permissive. Preliminary data suggest that at least two cell lineages arise following exposure to retinoic acid, and we are currently studying these by following the differential expression of a number of cell surface antigens. (M)